A problem associated with the use of nuts with fasteners and couplings is that of the nut backing off or loosening during use due to vibrational, environmental and other dynamic factors. This problem is particularly apparent in the aircraft industry where vibration and stress can cause loosening of fittings due to nut back-off.
Various methods are commonly used to resist unwanted nut back-off including, for example, locking washers, spring washers, prevailing torque threads, deformed threads, plastic thread inserts, arraerobic adhesives, double-nutting and locking pins.
For fluid couplings and the like, the most common method of preventing unwanted nut loosening is to use a safety wire to resist nut rotation. However, safety wire installation is costly because of the labor involved in affixing the safety wire to the nut and to an adjacent component after tightening of the nut. Also, the safety wire must be cut if the particular fitting requires routine retightening and/or maintenance or repair.
There are other known types of retention mechanisms for retaining the nut to the mating half (male half) of a fluid coupling. One such retention mechanism is disclosed in U.S. Pat. No. 5,215,336, and includes a serrated annular surface on a first member and fastening threads adjacent a bearing surface, and a flexible projection or projections or a complementary configuration to the serrated annular surface on a second member. The second member also includes fastening threads and a bearing surface. When the respective threads engage, they provide the primary preloading force to the bearing surface, while simultaneously the projections and serrated surface provide a retention force to insure a positive coupling.
Another such retention mechanism is disclosed in U.S. Pat. No. 6,557,900, and includes a nut locking device for locking a nut to the female coupling half of a coupling assembly. This has the advantage that the locking female assembly can be used with standard male fittings made by virtually all manufacturers and also retrofitted on fittings used in previously installed fluid couplings.
However, there is a continuing need for a retention mechanism for a coupling assembly that is simpler in construction than previous known retention mechanisms and provides a desired amount of resistance to back-off of the coupling assembly during use and still permits the coupling assembly to be disassembled when needed for maintenance and/or repair and reassembled as many times as desired.
Also there is a need for such a retention mechanism that prevents the back-off torque of the coupling assembly from dropping below a predetermined level even after the coupling assembly has been assembled and disassembled a number of times.